Professor Daniela Bortoletto

Abstract:

Drell-Yan lepton pairs are produced in the process p̄p→e +e-+X through an intermediate γ*/Z boson. The lepton angular distributions are used to provide information on the electroweak-mixing parameter sin2θw via its observable effective-leptonic sin2θw, or sinâ¡2θefflept. A new method to infer sin 2θw or, equivalently, the W-boson mass MW in the on-shell scheme, is developed and tested using a previous CDF Run II measurement of angular distributions from electron pairs in a sample corresponding to 2.1 fb-1 of integrated luminosity from p̄p collisions at a center-of-momentum energy of 1.96 TeV. The value of sinâ¡2θefflept is found to be 0.2328±0.0011. Within a specified context of the standard model, this results in sin 2θw=0.2246±0.0011, which corresponds to a W-boson mass of 80.297±0.055 GeV/c2, in agreement with previous determinations in electron-position collisions and at the Tevatron collider. © 2013 American Physical Society.

Abstract:

The first measurement of the electroweak production cross section of a Z boson with two jets (Zjj) in pp collisions at √s = 7TeV is presented, based on a data sample recorded by the CMS experiment at the LHC with an integrated luminosity of 5fb-1. The cross section is measured for the ℓℓjj (ℓ = e, μ) final state in the kinematic region m ℓℓ > 50 GeV, mjj > 120 GeV, transverse momenta pjT > 25 GeV and pseudorapidity |ηj| < 4.0. The measurement, combining the muon and electron channels, yields σ = 154 ± 24 (stat.) ± 46 (exp. syst.) ± 27 (th. syst.) ± 3 (lum.) fb, in agreement with the theoretical cross section. The hadronic activity, in the rapidity interval between the jets, is also measured. These results establish an important foundation for the more general study of vector boson fusion processes, of relevance for Higgs boson searches and for measurements of electroweak gauge couplings and vector boson scattering.

Abstract:

A search for supersymmetry is presented based on events with large missing transverse energy, no isolated electron or muon, and at least three jets with one or more identified as a bottom-quark jet. A simultaneous examination is performed of the numbers of events in exclusive bins of the scalar sum of jet transverse momentum values, missing transverse energy, and bottom-quark jet multiplicity. The sample, corresponding to an integrated luminosity of 19.4fb-1, consists of proton-proton collision data recorded at a center-of-mass energy of 8TeV with the CMS detector at the LHC in 2012. The observed numbers of events are found to be consistent with the standard model expectation, which is evaluated with control samples in data. The results are interpreted in the context of two simplified supersymmetric scenarios in which gluino pair production is followed by the decay of each gluino to an undetected lightest supersymmetric particle and either a bottom or top quark-antiquark pair, characteristic of gluino mediated bottom- or top-squark production. Using the production cross section calculated to next-to-leading-order plus next-to-leading-logarithm accuracy, and in the limit of a massless lightest supersymmetric particle, we exclude gluinos with masses below 1170GeV and 1020GeV for the two scenarios, respectively. © 2013 CERN.